Patent document 1 discloses a conventional audio signal reproduction apparatus which generates high-order harmonic components based on a signal read from a recording medium and adds them to the read signal to realize a natural sound reproduction. FIG. 18 shows a configuration of the audio signal reproduction apparatus. In FIG. 18, the audio signal reproduction apparatus includes a low pass filter 171, a harmonic generating circuit 174 composed of an absolute-value circuit 173 and a multiplier 172, a high pass filter 175, an adder 176, and a D/A converter 177.
A digital audio signal inputted via an input terminal T1 is subjected to oversampling processing in the low pass filter 171. Then, the harmonic generating circuit 174 including the absolute value circuit 173 and the multiplier 172 generates harmonic signals based on an audio signal generated by the oversampling processing. The high pass filter 175 allows only high frequency components of the generated harmonic signal to pass through the filter 175. The adder 176 adds the output signal from the high pass filter 175 to the audio signal generated by the oversampling processing. The D/A converter 177 converts the added audio signal to an analogue signal, thus generating an audio signal of which band is expanded or widened and outputting the band expanded audio signal via an output terminal T2.    Patent document 1: JP-A-07-93900